Thank you Vladimir 

What I understood from your answer is gradient copolymers are possible using two different reactivity monomers.  Would be there no effect of what type of polymerisation utilized? 

The phenomenon you mentioned is for gradient copolymers in which more active monomer reacts faster, However , decreasing its concentration in residual feed,  results the incorporation of less reactive monomer into polymer chain . so copolymer would be gradient having end chains of less reactive monomers.

Gradient copolymers  are very common in living polymerisation (CRP, ATRP etc) while I could not find any example of it using aromatic nucelophilic substitution polymerisation. 

My assumption is a polyether sulfone/ketone/bisphenol type polymerization (dichlorodiphenyl sulfone –fast-- and 4,4’-diclorobenzophenone-slow).  During step growth polymerization,predominantly low MW oligomers form up to 75% monomer conversion.  These would most likely incorporate the faster reacting monomer (DCDPS) preferentially.  As the reaction moves to higher conversion, the slower monomer (DCBP) will most likely link two oligomers to make a higher MW oligomer/polymer.  I propose a single (DCBP) will react between two relatively larger sequences of oligomers containing primarily DCDPS.  The slower reacting monomer (DCBP) will be more isolated in the chain compared to larger sequences containing the faster reacting monomer (DCDPS).  Controlling the incorporation of the (DCBP) slower reacting monomer into gradient sequences would seem difficult.  You could make a low MW bisphenol capped oligomer by stoichiometric offset containing only the slower reacting monomer (DCBP) and excess bisphenol.  You could use it as a component in a subsequent reaction with the faster reacting monomer (DCDPS) and bisphenol to make pseudo blocks of the DCBP monomer.  (These could be made to several different target molecular weights.)  By altering the total content of the DCBP oligomer from 5 to 40% in a second polymer, the “blocks” could be altered as macroscopic sequences of both fast and slow reacting monomers.  I say macroscopic sequences since there would still be a distribution of sequence lengths in the low MW oligomer precursor since a polydispersity of ~2 exists.  Controlling how each length oligomer (3-,5-,10- mer) incorporates predictably/reliably seems to me, difficult.  Directionally, a 2-step polymer sequence like this could provide some insight.

Thank you very much Michael for your detailed answer.

The sequencing of monomers is much clear to me now, and it really seems difficult of gradient arrangement of monomers in polymer chain. The reason for my question was a thesis, in which author reported gradient type polymer by aromatic nucleophilic substitution by controlling reaction conditions and minimized the difference of electrophile reactivity, NMR spectra are provided as evidence (https://etd.ohiolink.edu/rws_etd/document/get/wright1222006664/inline). I am using bischloro-terminated naphthalimide and phthalimide containing monomers and there is not any study reported about their reactivity.